This invention relates to the test and alignment of color television receivers which are in the final stages of production. Specifically, apparatus and methods are provided for establishing the color temperature of a color television receiver in a rapid and expeditious manner.
Color television receivers require a number of adjustments during the final phases of manufacture before delivering the receiver to a consumer. In the past, one of the more time consuming adjustments was establishing the proper picture tube color temperature. The difficulty in achieving the proper color temperature results from differences in the efficiency of the apparatus used for generating each of the primary colors. Color temperature has been achieved in the past by having an operator adjust the relative outputs from the receiver R, G and B amplifiers until a proper color is displayed. This technique is, however, very subjective and varies from person to person. Also, the color temperature of the picture changes depending upon the brightness level of a given scene. Therefore, two adjustments for color temperature are provided, one for high brightness levels and another for low brightness levels.
Generation of the primary colors in a picture tube is accomplished by selectively exciting a phosphor surface. The phosphor surface comprises alternate dots or stripes of different colored light emitting phosphors. The phosphor stripes or dots give off red, green or blue light when selectively excited by one of three electron guns. The phosphors which produce light of different colors have different light producing efficiencies. Therefore, the electron gun which illuminates a phosphor having a low light producing efficiency must be driven with a signal having a greater amplitude than an electron gun which illuminates a higher efficiency phosphor for producing a different color.
Adding to the inherent differences in efficiency of different color producing phosphors are differences in efficiencies of the electron guns which produce the electron beam for selectively exciting the phosphors which produce the different colors. These differences in efficiencies must also be compensated for by applying different levels of input signals to the respective electron guns.
Another problem which occurs in establishing color temperature are changes in the brightness of the picture tube which affects the color temperature. Therefore, a means for holding the brightness level constant during the color temperature adjustment is desirable.